Patent GB-724126-A (GB)
Title: Improvements in and relating to ferroelectric ceramic compositions
Filed: 1952-06-05
Abstract: A ferroelectric material, capable of activation to exhibit piezoelectric properties comprises a vitrified combination of niobium pentoxide and lead oxide, according to the formula (PbO)x. Nb2O5, where x lies between 0.5 and 1.5 and is preferably about 1.  This material is produced by preparing a correspondingly proportioned mixture of lead sulphate and niobium pentoxide, and subjecting the formed mixture without previous heating to rapid firing at a temperature between 1250 and 1325 DEG C., preferably 1300 DEG C., in an oxidizing atmosphere until vitrification of the lead oxide and the niobium pentoxide occurs. It is advantageous to add titanium dioxide or zirconium oxide in amounts up to 17 per cent of the lead niobate content to act as a flux and improve the properties of the product. In obtaining the products of the invention the steps described are: (1) mixing materials in a liquid such as acetone or amyl acetate, (2) drying, (3) pulverizing to pass a 100 mesh B.S.S. screen, (4) pressing into moulds with or without a plasticizer such as a 10 per cent polyvinyl alcohol solution in water, or extrusion, or casting, (5) rapid firing by introducing the formed piece directly into the hot zone of a furnace operating at 1300 DEG C., and maintaining it therein for 45 minutes, and (6) cooling.  Regrinding, reforming and refiring may be necessary.  The product may then be piezoeltctrically activated.  A preferred composition is prepared from materials providing 50 mol per cent. PbO, 47.5 mol per cent. Nb2O5, and 2.5 mol per cent. ZrO2; other compositions are specified.ALSO:A ferro-electric material, capable of activation to exhibit piezo-electric properties comprises a vitrified combination of niobium pentoxide and lead oxide, according to the formula (PbO)x, Nb2O5, where x lies between 0.5 and 1.5 and is preferably about 1. This material is produced by preparing a correspondingly proportioned mixture of lead sulphate and niobium pentoxide, and subjecting the formed mixture without previous heating to rapid firing at a temperature between 1,250 and 1,325 DEG C., preferably 1,300 DEG C., in an oxidizing atmosphere until vitrification of the lead oxide and the niobium pentoxide occurs. It is advantageous to add titanium dioxide or zirconium dioxide in amounts up to 17 per cent. of the lead niobate content to act as a flux and improve the properties of the product.  In obtaining the products of the invention the steps described are: (1) mixing materials in a liquid such as acetone or amyl acetate; (2) drying; (3) pulverizing to pass a 100 mesh B.S.S. screen; (4) pressing into moulds with or without a plasticizer such as a 10 per cent. polyvinyl alcohol solution in water, or extrusion, or casting; (5) rapid firing by introducing the formed piece directly into the hot zone of a furnace operating at 1,300 DEG C., and maintaining it therein for 45 minutes; and (6) cooling.  Regrinding, re-forming and refiring may be necessary.  A preferred composition is prepared from materials providing 50 mol per cent. PbO, 47.5 mol per cent. Nb2O5, and 2.5 mol per cent. ZrO2; other compositions are specified.